Your heart is racing, and you feel the sweat pouring down the side of your neck, but you need to hang on for 15 more seconds to make it through this high-intensity interval. The interval buzzer goes off. Whew! You made it!
Such is the nature of high-intensity interval training or HIIT, a form of exercise that alternates between periods of high-intensity work and active rest or low-intensity work. High-intensity interval training offers many of the benefits as other forms of exercise, but with less time, less effort, and, often, better results in terms of weight loss and weight control. In fact, some studies show HIIT is more effective for fat loss than conventional endurance training.
Why put yourself through such a workout? Many people do high-intensity interval training, or HIIT training, to burn calories to lose weight. Some even launch into a HIIT workout because they enjoy the added challenge of pushing themselves, but there’s another reason to add HIIT training to your fitness agenda. Scientists say that intense exercise may have more benefits for heart health than exercising at a moderate intensity and now they know why.
What a Recent Study Showed about HIIT Training and Heart Health
Why might high-intensity interval training offer more heart health benefits? Researchers at the Norwegian University of Science and Technology focused at a more granular level on the impact vigorous exercise has on cells that make up the heart, specifically cells in the sinoatrial node, a portion of the heart known as the pacemaker of the heart.
It’s cells in the sinoatrial node that initiate each heartbeat by creating an action potential, a nerve impulse, that spreads to other heart cells. This sequence of events causes the heart to contract, as it does each time your heartbeats. Once the sinoatrial node sends an action potential to other heart cells, calcium flows into the heart cells to initiate the contraction. So, the flow of calcium is critical for initiating heartbeats and for a healthy heart rhythm.
What does this have to do with high-intensity exercise? Scientists believe that high-intensity exercise boosts the flow of calcium into the heart cells with each heartbeat and enhances how heart cells handle calcium. Therefore, intense exercise causes your heart to become more efficient at initiating contractions of the heart.
When people have heart failure, calcium doesn’t flow into heart cells as effectively with each action potential, and the heart muscle contracts with less force. The calcium may even leak out of the heart cells. As heart failure worsens, the heart contracts with less and less force to the point that fluid starts to build up in tissues as the heart muscle weakens and circulation slows.
High-Intensity Interval Training and Heart Failure
Researchers at the Norwegian University of Science and Technology found that high-intensity exercise can reverse these dysfunctions in people with heart failure and increase the pumping power of the heart. In rats with heart failure, interval training where the rats exercised at 90% of their maximum at 4-minute intervals, experienced significant improvements in how much blood their heart pumped with each beat. As you might guess, they also got fitter.
In the study, the rats who did high-intensity interval training also became more resistant to a dangerous abnormal heart rhythm called ventricular fibrillation that causes the heart to beat weakly and irregularly and can lead to death. Ventricular fibrillation is a medical emergency that can lead to asystole, where the heart and blood flow to the body ceases.
How did moderate-intensity exercise compare to HIIT in this study? When rats with heart failure did moderate-intensity exercise, they had to exercise longer to get benefits and they didn’t get the full “perks” that high-intensity exercise offered. Their heart-pumping power improved only half as much as they didn’t experience the same degree of protection against ventricular fibrillation.
Other Reasons High-Intensity Exercise Is Healthy for the Heart
Although you might think high-intensity interval training places more stress on the heart than exercising at a moderate intensity, that’s not necessarily the case. More cardiologists are recommending high-intensity interval training for people who have had a heart attack in the form of cardiac rehab after studies show this type of training is less stressful to the heart than long periods of moderate-intensity exercise. It also may be better for increasing aerobic capacity in people with stable cardiovascular disease. Of course, it’s a workout that heart patients should always do under supervision.
Another 8-week study in older adults found those who engaged in high-intensity interval training enjoyed greater health improvements, including larger gains in aerobic capacity and improved insulin sensitivity. Both of these are beneficial for heart health and for lowering the risk of cardiovascular disease.
The Bottom Line
High-intensity interval training is a more time-efficient way to work out and there’s evidence that working out in this manner may be more beneficial for heart health and lowering the risk of cardiovascular disease. Although HIIT workouts are short and intense, they’re designed to improve cardiovascular fitness, burn fat, and tone the body, and do it in less time. So, the next time you’re sweating through a high-intensity interval, think about the good things it’s doing for your heart and blood vessels.
- Exercise training reveals micro-RNAs associated with improved cardiac function and electrophysiology in rats with heart failure after myocardial infarction. Journal of Molecular and Cellular Cardiology, 2020; 148: 106 DOI: 10.1016/j.yjmcc.2020.08.015.
- com. “What makes hard workouts so effective?”
- “Interval training for a stronger heart – Harvard Health.” https://www.health.harvard.edu/exercise-and-fitness/interval-training-for-a-stronger-heart.
- “7 Reasons Why HIIT Is Good For Your Heart – weightlessMD.” https://weightlessmd.com/7-reasons-hiit-good-heart/.
- “High-intensity interval training for health benefits and ….” https://pubmed.ncbi.nlm.nih.gov/31565193/.
- org. “High-intensity Interval Training for Active Older Adults”
- Hannan AL, Hing W, Simas V, et al. High-intensity interval training versus moderate-intensity continuous training within cardiac rehabilitation: a systematic review and meta-analysis. Open Access J Sports Med. 2018;9:1-17. Published 2018 Jan 26. doi:10.2147/OAJSM.S150596.
- Hwang CL, Yoo JK, Kim HK, Hwang MH, Handberg EM, Petersen JW, Christou DD. Novel all-extremity high-intensity interval training improves aerobic fitness, cardiac function and insulin resistance in healthy older adults. Exp Gerontol. 2016 Sep;82:112-9. doi: 10.1016/j.exger.2016.06.009. Epub 2016 Jun 21. PMID: 27346646; PMCID: PMC4975154.